docstr: check zero crossing rate on a buffer with an impulse 
docstr_tok: ["check","zero","crossing","rate","on","a","buffer","with","an","impulse"]
code: def test_impulse(self):
      """check zero crossing rate on a buffer with an impulse"""
      self.vector[int(buf_size / 2)] = 1.0
      self.assertEqual(0.0, zero_crossing_rate(self.vector))
  
file_path: aubio/python/tests/test_zero_crossing_rate.py
imports: from numpy.testing import TestCase
  from aubio import fvec, zero_crossing_rate
label_desc: Use image node_id 4 for calling the zero_crossing_rate_test_case obj's underlying member method code with example usage: obj.test_impulse() without return types